This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Lendzian, K. J. Search for Related Content PubMed PubMed Citation Articles by Lendzian, K. J. Agricola Articles by Lendzian, K. J.

Articles

Metabolism of Specifically Labeled Glucose, Glucose 1-Phosphate, and Glucose 6-Phosphate via the Oxidative Pentose Phosphate Cycle in a Reconstituted Spinach Chloroplast System in Darkness and in the Light ¹

Institut für Botanik und Mikrobiologie, Lehrstuhl für Botanik, Technische Universität, D-8000 München 2, Federal Republic of Germany

Using isolated spinach (hybrid 424) chloroplasts deprived of their envelopes (reconstituted chloroplast system), the metabolism of glucose, glucose 1-phosphate, and glucose 6-phosphate via the oxidative pentose phosphate cycle was analyzed. The activity of oxidative pentose phosphate cycle was monitored by continuous sampling of the CO₂ released during the decarboxylation process of 6-phosphogluconate.

The rate of CO₂ released in the dark from [C-1-¹⁴C]glucose 6-phosphate was 4 to 6 micromoles per milligram chlorophyll per hour. A CO₂ release from the C-6 position of [C-6-¹⁴C]glucose 6-phosphate was hardly measurable within 60 minutes of incubation. Glucose 1-phosphate was readily converted to glucose 6-phosphate without externally added glucose bisphosphate and was metabolized via the oxidative pentose phosphate cycle. The phosphorylation of glucose to glucose 6-phosphate was mediated by hexokinase present in the reconstituted system. This step was rate-limiting for the over-all reaction of the oxidative pentose phosphate cycle with glucose being the substrate (0.5 micromoles per milligram chlorophyll per hour). Addition of hexokinase increased the rate of CO₂ release to 5 micromoles per milligram chlorophyll per hour.

The flow of carbon through the oxidative pentose phosphate cycle was greatly reduced upon the addition of NADPH and ATP. Whereas NADPH inhibited the metabolism of [C-1-¹⁴C]glucose 6-phosphate via the oxidative pentose phosphate cycle, ATP stimulated carbon flow into the 3-phosphoglycerate, dihydroxyacetone phosphate, and bisphosphates pools via the glycolytic pathway mediated by phosphofructokinase. This regulatory phenomenon could also be demonstrated with the reconstituted system undergoing a dark-light-dark transition. Data are presented indicating the conditions under which glucose 6-phosphate or glucose 1-phosphate are metabolized via the oxidative pentose phosphate cycle and the glycolytic pathway.